JP2840677B2 - Method for producing yttrium oxysulfide phosphor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an yttrium oxysulfide-based phosphor used for a phosphor screen or the like of a cathode ray tube, and in particular, to a yttrium oxysulfide-based phosphor having high brightness and small particle size. The present invention relates to a method for enabling production of a phosphor.

[Summary of the Invention]

The present invention relates to the production of yttrium oxysulfide-based phosphor used for the phosphor screen of a cathode ray tube or the like, wherein sodium carbonate and sulfur as fluxes are 2 to 10 times and 4 to 20 times the number of moles of yttrium oxide, respectively. And a molar excess of sodium carbonate to sulfur of 0.2 to
An object of the present invention is to provide a method for obtaining a high-brightness, small-particle-diameter yttrium oxysulfide-based phosphor by a simple operation by firing the composition of 1.25 at 900 to 1100 ° C.

[Conventional technology]

It is known that yttrium oxysulfide (Y ₂ O ₂ S) becomes a red or green phosphor (hereinafter, referred to as an yttrium oxysulfide phosphor) when activated with a rare earth element such as samarium, europium, and terbium. It is used for a phosphor screen of a projection type cathode ray tube and a cathode ray tube for a view finder of a video camera.

As a method for producing the yttrium oxysulfide-based phosphor, a substance capable of forming a sulfide or polysulfide of an alkali metal in a firing process, that is, a mixture of sodium carbonate and sulfur, sodium thiosulfate, potassium sulfide, or the like is used as a flux. A method is generally used in which the mixture is mixed with a compound containing yttrium oxide (Y ₂ O ₃ ) and an activator and fired.

[Problems to be solved by the invention]

By the way, there are various factors which influence the characteristics of the yttrium oxysulfide-based phosphor. Among them, a cathode ray tube having a phosphor pattern with a finer particle size such as a recent high-definition vision or the like has a particle size, a particle size distribution, and a purity. This is an extremely important factor in realizing high resolution, high image quality, and high luminance. However, according to the conventional manufacturing method, the volume average diameter of the yttrium oxysulfide-based phosphor obtained is approximately 4 μm or more, and the phosphor having a smaller particle diameter than that required for realizing the above-described cathode ray tube has a high purity ( It is extremely difficult to obtain a single-phase compound having a high luminance. Therefore, conventionally, only the fine particles having a diameter of less than 4 μm have been classified from the synthesized particles having a relatively large average particle diameter. However, this classification step requires a complicated operation and lowers the yield of the phosphor, which is not preferable from the viewpoint of productivity and economy.

Accordingly, an object of the present invention is to provide a method for obtaining an yttrium oxysulfide-based phosphor with high brightness and small particle size by a simple operation.

[Means for solving the problem]

The present inventors have studied to achieve the above object, and as a result, in the production of yttrium oxysulfide-based phosphor,
By adding a large excess of sulfur and sodium carbonate as fluxing agents to yttrium oxide in a predetermined molar ratio within a predetermined range, respectively, and optimally selecting a calcination temperature, a single-phase, small-particle acid is obtained. The present inventors have found that yttrium sulfide can be obtained with high reproducibility and high yield, and have completed the present invention.

That is, the method for producing an yttrium oxysulfide-based phosphor according to the present invention comprises adding at least 2 to 10 times mol of sodium carbonate and 4 to 20 times mol of sulfur with respect to yttrium oxide; When firing a composition in which the molar ratio of sulfur to sulfur is 0.2 to 1.25, the molar ratio of sodium carbonate to sulfur is Na ₂ CO ₃ / S, and the firing temperature is T. 1000 ° C <T ≦ 1100 ° C when sodium is 2 moles or more and 0.2 ≦ Na ₂ CO ₃ /S<0.5, when sodium carbonate is 3 moles or more for yttrium oxide and Na ₂ CO ₃ /S=0.5 900 ℃
≦ T ≦ 1100 ° C, 900 ° C in case of 0.5 <Na ₂ CO ₃ /S≦1.25, 3 times or more sodium carbonate to yttrium oxide
Satisfies the condition of T <1000 ° C. If the firing temperature T exceeds 1000 ° C, the firing time should be 3 hours or less, and if the firing temperature T exceeds 1050 ° C, the firing time should be 1 hour or less. It is characterized by the following.

In the production method of the present invention, first, sodium sulfide (Na ₂ S) or sodium polysulfide (Na ₂ S _x , where x is an integer of 2 to 5) is produced by the reaction between sulfur as a flux and sodium carbonate. It is based on a reaction that reacts with yttrium oxide to produce yttrium oxysulfide (Y ₂ O ₂ S). Therefore, sulfur need not necessarily be added in a simple form. The above ranges of the amounts of sulfur and sodium carbonate added are all set from the viewpoint of optimizing the characteristics of the yttrium oxysulfide-based phosphor to be generated,
If it is lower than the above range, the product will not be a single phase,
The particle size becomes too large or both disadvantages occur. Further, even if it exceeds the above range, the effect of addition does not change, so that it is not practical. Further, the molar ratio between sodium carbonate and sulfur is also selected in the optimum range. If the molar ratio is outside the above range, the purity tends to decrease and the particle size tends to increase.

As the flux, in addition to the above sodium carbonate and sulfur, it is preferable to use a phosphate in a molar amount of 1/1000 to 10 times the amount of yttrium oxide. Examples of the phosphate include ammonium hydrogen phosphate, sodium hydrogen phosphate,
Sodium phosphate, potassium hydrogen phosphate, potassium phosphate and the like can be used.

Further, in addition to the yttrium oxide and the flux, a compound serving as a source of the activating element is usually added to the composition.
The activating elements include samarium and europium for obtaining a red phosphor, terbium for obtaining a green phosphor, and the like. These elements are mainly added in the form of oxide.
Since the amount of addition varies according to the desired chromaticity, it may be appropriately determined within the range of the amount of addition generally used in the field of manufacturing rare earth phosphors, but it is approximately 1/1000 to 1/1 / about yttrium oxide. It is 5 times the molar amount.

Further, in order to alleviate the luminance saturation phenomenon, a trace amount of a rare earth element such as terbium or praseodymium is added, and these are finally added to the yttrium oxysulfide by 20 to 30 wt.
You may make it take in in the range of ppm.

The firing temperature is selected in the range of 900 to 1100 ° C. If the temperature is lower than 900 ° C., the luminance of the obtained yttrium oxysulfide-based phosphor is insufficient due to insufficient stoichiometric incorporation of sulfur, remaining unreacted raw materials, and non-uniform crystal structure. More preferably, the lower limit is 950 ° C. On the other hand, if the temperature exceeds 1100 ° C., the particle size becomes large, and a compound in which a part of yttrium in yttrium oxide is replaced with europium may be formed, which may lower the purity, which is not preferable.

In addition, to obtain a single-phase yttrium oxysulfide, 900 to 1100, depending on the molar ratio of sodium carbonate and sulfur
A more appropriate temperature must be selected in the range of ° C. That is, the molar ratio between sodium carbonate and sulfur is Na ₂ C
When O ₃ / S and the firing temperature are T, 1000 ° C <T ≦ 1100 ° C when 0.2 ≦ Na ₂ CO ₃ /S<0.5, 900 ° C ≦ T when Na ₂ CO ₃ /S=0.5 In the case of ≦ 1100 ° C. and 0.5 <Na ₂ CO ₃ /S≦1.25, it is necessary to satisfy the condition of 900 ° C. ≦ T <1000 ° C. 0.2 ≦ Na ₂ CO ₃ / S <
In the case of 0.5, the firing temperature is set to 1000 ° C or less, or
When 0.5 <Na ₂ CO ₃ /S≦1.25, if the sintering temperature is set to 1000 ° C. or higher, single phase yttrium oxysulfide cannot be obtained.

The firing time is not particularly limited as long as the above conditions are satisfied, and the firing time generally applied in the field of manufacturing rare earth phosphors can be applied, and is set to about 1 to 5 hours.

[Action]

In the production method of the yttrium oxysulfide-based phosphor of the present invention, the amount of the flux to yttrium oxysulfide, the molar ratio of the flux components, and the firing temperature are selected optimally, so that the conventional process is greatly reduced. A single-phase phosphor having a small particle size can be obtained in high yield without changing the phosphor.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental results.

First, the conditions under which europium-activated yttrium oxysulfide was formed in a single phase under a constant firing temperature and a constant firing time were examined.

0.1 mol yttrium oxide, 3.85 mmol europium oxide (Eu ₂ O ₃ ), 20 ppm terbium oxide (Tb ₂ O ₃ ) based on yttrium oxide, 0.2-3.5 mol sulfur, 0.1-1.0 mol sodium carbonate , And 0.03
Molar ammonium hydrogen phosphate was weighed and mixed, and the mixture was filled in an alumina crucible. Next, the above mixture was baked at a temperature of 1100 ° C., 1000 ° C. or 900 ° C. for 1 hour, washed with water, filtered and dried to obtain europium-activated yttrium oxysulfide powder. An X-ray diffraction spectrum and an emission spectrum of the obtained powder by CuKα radiation were measured to determine whether the powder was a single phase.

The results are shown in FIGS. 1 (A) to 1 (C). In these figures, the vertical axis is the number of moles of sodium carbonate (Na ₂ CO ₃ ),
The number of moles of sulfur (S) is plotted on the horizontal axis, and the case where the produced powder is recognized as a single phase is represented by a plot of ○, and the case where the generated powder is not recognized as a single phase is represented by a plot of ×. is there. FIG. 1A corresponds to the case where the firing temperature is 1100 ° C., FIG. 1B corresponds to the case where the firing temperature is 1000 ° C., and FIG.

First, when the calcination temperature is 1100 ° C., as shown in FIG. 1 (A), sodium carbonate is 0.2 mol or more with respect to 0.1 mol of yttrium oxide, and the molar ratio of sodium carbonate to sulfur (hereinafter referred to as Na). ₂ CO ₃ / S) 0.2-0.5
A single phase is achieved in the range. When the sintering temperature is 1000 ° C., as shown in FIG.
A single phase has been achieved with more than 2 moles and with Na ₂ CO ₃ /S=0.5. Further, when the sintering temperature is 900 ° C., as shown in FIG. 1 (C), a single phase is achieved when the amount of sodium carbonate is 0.3 mol or more and Na ₂ CO ₃ /S=0.5 to 1.25. I have.

Here, whether or not the obtained powder was a single phase was determined based on the following fact on the spectrum.

First, FIG. 2 shows an X-ray diffraction diagram of the powder indicated by plot a in FIG. 1 (C). The vertical axis is the diffraction intensity (relative scale),
The horizontal axis represents the diffraction angle 2θ (°), and the number in parentheses near each peak represents the surface index of the diffraction surface. From this figure, it can be seen that the powder is a single-phase, hexagonal, europium-activated yttrium oxysulfide (including a trace amount of terbium; the same applies hereinafter).

On the other hand, the X-ray diffraction pattern of single-phase, cubic yttrium oxide as a raw material shows a completely different pattern as shown in FIG.

When the powder obtained after the calcination is not a single phase, a change in the pattern appears such that a part of the peak in FIG. 3 is added to the peak in FIG. 2 or a completely different peak appears. For example, the X-ray diffraction pattern of the powder shown by plot b in FIG. 1 (C) is as shown in FIG. It is almost similar to the pattern of FIG. 2, and it is suggested that most of the product is the target product. However, a small peak, which seems to be a diffraction peak from the (411) plane of yttrium oxide, is slightly present near 2θ = 34 °. It does not appear to be completely monophasic. The X-ray diffraction pattern of the powder shown by plot c in FIG. 1 (A) is as shown in FIG. In this figure, in addition to the peak derived from the target product and the raw material yttrium oxide, some small peaks which are considered to be derived from europium-activated yttrium oxide appear, and the purity is extremely low.

From the above, in the measurement of the X-ray diffraction spectrum, the pattern of FIG.

Further, the determination as to whether or not a single phase can be made based on the emission spectrum. For example, the emission spectrum of the powder shown by the plot a in FIG. 1 (C) is as shown in FIG. 6, and when a single-phase hexagonal europium-activated yttrium oxysulfide is obtained, A pattern having a main peak at 627 nm appears. The chromaticity of this powder is represented by x = 0.634 and y = 0.347 in color coordinates. In contrast,
The emission spectrum of the powder shown by plot c in FIG. 1 (A) is a pattern having a main peak at 612 nm as shown in FIG. The chromaticity of this powder is x in color coordinates
= 0.641, y = 0.351, indicating that a product having a different chromaticity from that of FIG. 6 is apparently obtained.

From the above, in the measurement of the emission spectrum,
The pattern shown in FIG. 6 was used as a guide for the formation of a single phase.

The results of FIGS. 1 (A) to 1 (C) were converted to Na ₂ CO ₃
FIG. 8 is a graph plotted again to represent the correlation between the value of / S and the firing temperature. In the figure, the vertical axis represents the firing temperature (° C.), and the horizontal axis represents Na ₂ CO ₃ / S. Here, the abscissa represents the molar ratio of the flux components, and does not represent the actual amount used. From this figure, it can be seen that the molar ratio of the flux component when a single phase is achieved tends to decrease as the firing temperature increases.
With Na ₂ CO ₃ /S=0.5, a single phase was achieved at all firing temperatures.

Therefore, when Na ₂ CO ₃ /S=0.5, which is considered to have a relatively large chance of achieving a single phase at any temperature, and Na _{2, which} is considered to be difficult to achieve a single phase in the range of the experiments so far, In the case of CO ₃ /S=0.13, the achievement of the single phase when the firing time was extended to 3 hours was examined. Firing temperature is 11
There were four types: 00 ° C, 1000 ° C, 950 ° C, and 900 ° C. The results are shown in FIGS. 9 (A) and 9 (B). In each figure, the vertical axis represents the firing temperature (° C.), and the horizontal axis represents sodium carbonate (Na).
₂ (CO ₃ ) and sulfur (S), respectively. FIG. 9 (A) shows Na ₂ CO ₃ /S=0.5, and FIG. 9 (B) shows Na ₂ CO ₃ /S=0.1.
3 represents each case.

According to these figures, in the composition of the flux in which a single phase was not achieved in the firing time of 1 hour, the single phase was achieved regardless of the value of Na ₂ CO ₃ / S even when the firing time was set to 3 hours. Absent. Further, it can be seen that the formation of a single phase depends on both the molar ratio of the components of the flux and the amount of the flux used. Furthermore, Na ₂ CO ₃ / S
In the case of = 0.5, there is a tendency that a single phase is achieved with a smaller amount of flux as the firing temperature increases.

The above is a study on the purity of the obtained powder, but the present inventors have further studied the particle size.

First, corresponding to FIGS. 1 (A) to 1 (C), the relationship between the amount of each flux component used at each firing temperature and the particle size of the obtained powder was examined. The results are shown in FIGS. 10 (A) to 10 (C). In the figure, the vertical axis represents the number of moles of sodium carbonate (Na ₂ CO ₃ ), and the horizontal axis represents the number of moles of sulfur (S). Regarding the particle size, since a 4 μm yttrium oxysulfide-based phosphor has been obtained by a conventional technique, a smaller value of 3 μm was used as a criterion for evaluation. That is, the case of clearly smaller than 3 μm is indicated by a circle, the case of about 3 μm is indicated by a triangle, and the case of clearly larger than 3 μm is indicated by a cross. FIG. 10 (A) shows a firing temperature of 1100 ° C., FIG. 10 (B) shows a firing temperature of 1000 ° C., and FIG.
Each corresponds to the case of 900 ° C.

From these figures, it can be seen that the particles tend to grow larger as the firing temperature increases. Further, when these FIGS. 10 (A) to 10 (C) are superimposed on FIGS. 1 (A) to 1 (C), respectively, it can be seen that the single phase is confirmed. It can be seen that the reduction in particle size was also achieved.

Next, 0.4 mol of sodium carbonate was used, and Na ₂ CO ₃ /
When S = 0.5, the particle size of the yttrium oxysulfide-based phosphor obtained when the firing temperature was changed in the range of 900 to 1200 ° C. and the firing time was changed in the range of 1 to 6 hours was examined. The results are shown in FIG. In the figure, the vertical axis represents the firing temperature (° C.), and the horizontal axis represents the firing time (hour). From this figure, it can be seen that the particle size tends to increase as the firing temperature increases and the firing time increases.

Finally, in order to examine the practicality of the obtained powder as a phosphor material, the emission luminance was measured. The emission luminance was measured using a digital photometer J16 manufactured by Tektronix, which has visibility characteristics. Since it is extremely difficult to obtain the absolute value of the emission luminance of the powder sample, the evaluation was made based on the relative luminance when the emission luminance of a commercially available green phosphor was 100%.

First, FIG. 12 shows the results of examining the effects of the composition of the flux component and the firing temperature on the relative luminance of the obtained product when the firing time is 1 hour. In the figure, the vertical axis represents relative luminance (%), and the horizontal axis represents firing temperature (° C.). Line A is 0.1 mol and 0.2 mol respectively of sodium carbonate and sulfur per 0.1 mol of yttrium oxide, line B is 0.15 mol and 0.3 mol, and line C is 0.2 mol
Mole D and 0.4 mole, line D is also 0.3 mole and 0.6 mole, and line E is also 0.5 mole and 1.0 mole.
All correspond to Na ₂ CO ₃ /S=0.5).

According to this figure, when the molar ratio of the flux components is constant,
As the firing temperature increases, the relative luminance of the obtained powder tends to increase, and it can be seen that if the conditions are appropriately selected, a powder having a light emission luminance equal to or higher than that of a commercially available product can be prepared. However, even if the luminance is sufficient, attention must be paid to the fact that a single phase may not be formed, the chromaticity may change, or the particle size may increase due to an increase in the firing temperature.

Further, FIG. 13 shows the results of examining the effects of the composition of the flux component and the sintering time on the emission luminance of the product obtained when the sintering temperature was 1000 ° C. In the figure, the vertical axis represents relative luminance (%), and the horizontal axis represents firing time (hour). Line A
The meaning of the line E is the same as that of FIG. Further, the line F shows that the amount of sodium carbonate and the amount of sulfur used are each 0.4 mol per 0.1 mol of yttrium oxide.
In the case of 0.8 mol, the line G corresponds to the case of 0.05 mol and 0.35 mol, and the line H corresponds to the case of the same 0.45 mol and 3.5 mol.

Referring to this figure, it is generally observed that when the firing time is extended, with some exceptions, the relative luminance tends to increase. In this case, if the conditions are properly selected, the luminance is equal to or higher than that of a commercially available product. It can be seen that one can be prepared. However,
The above-mentioned single phase and particle size have the same meanings as the above-mentioned cautions.

Taking the above results into consideration, yttrium oxide 0.
0.2-1.0 sodium and 0.4 sulfur
When the firing temperature T is 0.2 ≦ Na ₂ CO ₃ /S<0.5, 1000 ° C. <T ≦ 1100 ° C. and Na ₂ CO 3 ₃ 900 / C when 0.5 / S = 0.5
900 ℃ ≦ T <when T ≦ 1100 ℃, 0.5 <Na ₂ CO ₃ /S≦1.25
It can be seen that when the condition of 1000 ° C. is satisfied, single-phase phosphor particles having a small particle size of 3 μm or less and high emission luminance can be obtained.

〔The invention's effect〕

As is clear from the above description, in the method for producing the yttrium oxysulfide-based phosphor of the present invention, the amount of the flux added to yttrium oxide, the composition of the flux component, and the firing temperature are optimally selected. A phosphor having high purity, high brightness, and extremely small particle size can be obtained in a high yield by a simple method. If the particle size of the phosphor is reduced, the surface roughness of the phosphor screen is reduced, and the reflectance of the metal back is improved, the defects such as pinholes are reduced, the packing density of the phosphor is improved, and the amount of the phosphor used is accordingly reduced. There are many advantages related to quality, productivity, and economic efficiency, such as reduction in cost, improvement in adhesion between the glass panel and the phosphor pattern, and sharpening of the contour of the phosphor pattern. Such an yttrium oxysulfide-based phosphor is extremely suitable for a projection type cathode ray tube requiring high resolution and high definition, a phosphor screen of a cathode ray tube for a viewfinder of a video camera, and the like.

[Brief description of the drawings]

1 (A) to 1 (C) are characteristic diagrams showing the phase purity of the phosphor obtained when the composition of the flux component is changed under a constant firing temperature and a constant firing time, FIG. 1 (A) corresponds to a case where the firing temperature is 1100 ° C., FIG. 1 (B) corresponds to a case where the firing temperature is 1000 ° C., and FIG. 2 to 5 are X-ray diffraction spectrum diagrams, and FIG.
Fig. 3 shows a single-phase yttrium oxysulfide phosphor powder synthesized according to the present invention, Fig. 3 shows an example of yttrium oxide used as a raw material, Fig. 4 shows an example of non-single-phase powder, and Fig. 5 shows a single-phase yttrium oxide powder. Other examples of unphased powder are shown. 6 and 7 are emission spectrum diagrams. FIG. 6 is a diagram showing a single-phase yttrium oxysulfide phosphor powder synthesized according to the present invention.
The figure shows an example of the powder that is not single-phased. 8th
The figure is a characteristic diagram showing the correlation between the molar ratio of the flux components, the firing time, and the phase purity under a constant firing time. 9 (A) and 9 (B) are characteristic diagrams showing the correlation between the amount of use of each flux, the firing temperature, and the single-phase formation under a constant flux ratio of the flux components and a constant firing time. There, FIG. 9 (a) in the case of Na ₂ CO ₃ /S=0.5, FIG. 9 (B) is corresponding to the case of Na ₂ CO ₃ /S=0.13. FIGS. 10 (A) to 10 (C) are characteristic diagrams showing the particle size of the powder obtained when the composition of the flux component is changed under a constant firing temperature and a constant firing time; Tenth
FIG. (A) shows a firing temperature of 1100 ° C., FIG. 10 (B) shows a firing temperature of 1000 ° C.
FIG. 10 (C) corresponds to the case where the temperature is 900 ° C., respectively.
FIG. 11 shows the use of 0.4 mol of sodium carbonate and the use of Na ₂ CO ₃ /
FIG. 4 is a characteristic diagram showing a correlation between a firing temperature, a firing time, and a particle size when S = 0.5. FIG. 12 is a characteristic diagram showing the relative luminance of powder obtained when fluxes of various compositions are used under a fixed firing time. FIG. 13 is a characteristic diagram showing the relative luminance of powder obtained when fluxes of various compositions are used at a constant firing temperature.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Katsutoshi Ohno 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-52-78784 (JP, A) 2-155984 (JP, A) (58) Fields studied (Int. Cl. ⁶ , DB name) C09K 11/00-11/89

Claims (1)

(57) [Claims] (1) at least 2 to yttrium oxide;
When calcining a composition in which 10 times molar amount of sodium carbonate and 4 to 20 times molar amount of sulfur are added and the molar ratio of sodium carbonate to sulfur is 0.2 to 1.25, When the molar ratio is Na ₂ CO ₃ / S and the sintering temperature is T, 1000 ° C <T ≦ 1100 when the molar ratio of sodium carbonate is twice or more of yttrium oxide and 0.2 ≦ Na ₂ CO ₃ /S<0.5. ℃, more than 3 times mol of sodium carbonate with respect to yttrium oxide, 900 ℃ ≦ T ≦ 1100 ℃ when Na ₂ CO ₃ /S=0.5, more than 3 times mol of sodium carbonate with respect to yttrium oxide, 0.5 <Na ₂ CO _{3 /} S ≦ 1.25, 900 ° C ≦ T <1000 ° C
Is exceeded, the firing time is 3 hours or less, and the firing temperature T is
A method for producing an yttrium oxysulfide-based phosphor, wherein the firing time is 1 hour or less when the temperature exceeds 1050 ° C.